Trospium is a quaternary ammonium derivative of tropine, and has anticholinergic properties. The hydrophilicity of the molecule, due to its permanent positive charge, limits its lipid solubility. Trospium chloride has been shown to antagonize acetylcholine on excised strips of human bladder muscle. Antispasmodic activity has been shown in the bladder, the small intestine, and on contractility of the gall bladder. Trospium chloride exhibits parasympatholytic action by reducing smooth muscle tone, such as is found in the urogenital and gastrointestinal tracts. This mechanism enables the detrusor to relax, thus inhibiting the evacuation of the bladder. Lowering the maximum detrusor pressure results in improved adaptation of the detrusor to the contents of the bladder, which in turn leads to enhanced bladder compliance with increased bladder capacity.
Trospium chloride was introduced into the market as a spasmolytic agent in 1967 (German patent 1 194 422). Trospium chloride has been available in an orally administrable, solid administration form (tablets and dragees), for intravenous or intramuscular injection as a solution, and for rectal administration as suppositories, and is primarily used for the treatment of bladder dysfunctions (urge incontinence, detrusor hyperreflexia). The product has been on the market in Germany and several other European countries for a number of years for specific therapeutic indications including urinary frequency, urgency, nocturia, and urge-incontinence associated with detrusor instability, urge syndrome, and detrusor hyperreflexia.
Currently, in the European market there is an immediate release trospium chloride tablet (Spasmo-lyt®), which is indicated for the treatment of urge incontinence and detrusor hyperreflexia and is used as a 20 mg tablet taken twice daily or bid (a total dose of 40 mg per day). In common with other quaternary ammonium compounds, orally administered trospium chloride is slowly absorbed, with the maximum blood level achieved after 5-6 hrs. The oral bioavailability is approximately 10%, and is significantly reduced with the intake of high-fat food. There are side effects associated with the use of the twice-daily trospium chloride regimen, such as dry mouth, headache, constipation, dyspepsia, and abdominal pain. These side effects are associated with a high blood concentration of trospium chloride. Moreover, studies in which a 40 mg immediate release dose was given once daily resulted in higher overall incidence of adverse events as compared to 20 mg given twice daily.
A once-a-day administration of trospium is advantageous over the twice-a-day administration in terms of both patient compliance and reduced adverse events, thus providing better treatment of the conditions for which trospium chloride is indicated.
In order to provide for an effective once-a-day form of trospium, there is a need for unique formulation approaches that provide the desired therapeutic effects while minimizing, if not eliminating, the undesired side effects mentioned above. This means that the minimum blood trospium concentration (Cmin) at steady state should be above the minimum therapeutically effective blood concentration and the maximum blood trospium concentration (Cmax) also at steady state should be below the maximum toxic blood concentration over the treatment period. Trospium chloride and other quaternary ammonium compounds exhibit a limited window of absorption in the human gastrointestinal tract, presenting a significant challenge to formulating a once-a-day composition.